Abstract

Sir Edward Bailey said that the paper concerned one of the most important subjects of present-day geological research. A reassessment was required wherever acid rock veined basic, etc. Discussion had been proceeding on these lines for a number of years. Analogies had been drawn between basic magma entering acid magma, and basic magma entering the sea. In some cases fuller analogy was afforded by the subglacial eruptions of Iceland, with their pillow-lavas, their melted ice, and their floods. Dr Doris Reynolds had drawn attention to this sort of thing in a paper on Slieve Gullion in 1937.

The Authors agreed with Sir Edward Bailey that a reassessment was indeed required of the time-relations and genesis whenever acid and basic rocks were intimately associated. They would like to acknowledge the important contributions that Sir Edward had made on the subject of acid-basic relationships. The analogy with subglacial eruptions mentioned by Sir Edward was in fact very close; it was a few days after having studied the products of a subglacial eruption in south-east Iceland that two of the authors reinterpreted the Austurhorn net-veined complex, so impressed were they by the similarities between the basic pillows, whole and broken, in each.

Dr J. F. Dewey said that the authors had presented excellent examples of contacts indicating the simultaneous intrusion and eruption of acid and basic magmas. The speaker had observed similar relationships in Lower Palaeozoic volcanic sequences in Ireland and North Wales. The Crogenen granophyre, south of the Mawddach estuary in Merionethshire,